Typically, valves (such as control valves or pressure regulators) are opened and closed by a pneumatic actuator. For example, a control fluid under pressure is introduced into a housing of the actuator, and the control fluid acts on a diaphragm that is coupled to a valve member of the control valve. An increase in pressure in the housing of the actuator may cause the valve member to displace toward a valve seat of the control valve, thereby closing the control valve. A decrease in pressure in the housing of the actuator may cause the valve member to displace away from valve seat of the control valve, thereby opening the control valve.
Typically, springs and air pressure within the pneumatic actuator are used to generate the loading force of the control valve. In some applications, electronic pressure regulators may be used in conjunction with pneumatic actuators to, for example, adjust the set point of the control valve. The electronic pressure regulator may use a small, variable pneumatic signal to pressure load the actuator or an amplifier to multiply the force generated by the signal. Accordingly, a small pneumatic signal (typically 0-100 psig) to control a large pressure (0-10,000 psig). However, errors associated with the electronic pressure regulator, the pressure transmitter used for sensing the set point, and the accuracy of the tuning are all amplified as well, thereby resulting in large fluctuations of the set point.